This invention relates in general to a gear box for transmitting power and, in particular, to a gear box for transmitting power wherein in the event the output drive shaft of the gear box is severed, the output drive mechanism will still be retained in the gear box to enhance safe operation.
More specifically, but without restriction to the particular embodiment and/or use which is shown and described for purposes of illustration, this invention relates to a gear box specially suited for adapting an automotive engine to a pusher-type propeller used for powering air-boats.
Air-boats are shallow draft water craft which are adapted for high speed movement over water which is too shallow for conventional boats. These air-boats are capable of movement over terrain such as ice and grasses, providing an extremely versatile vehicle capable of high speed movement over terrain which would be impassible to more conventional vehicles. Such air-boats are propelled by a motor-driven pusher propeller, which is positioned at the rear of the craft and above the boat hull to provide a pushing force for propelling the craft over water, ice, grasses etc. The hull of such water craft have a substantially flat or slightly curved bottom with a slightly raised bow, and generally draw very little water.
While air-boating began as a recreational sport, such vehicles are now found to have many applications including use as rescue vehicles and utility vehicles for conservation departments. Through their operational versatility air-boats provide access to many areas heretofore considered inaccessible. As air-boating has become ever increasingly popular, it has become necessary to provide a readily accessible source of engines for use in these vehicles, as well as a readily available source of parts for engine repair. Heretofore internal combustion aircraft engines have been used to power these vehicles, but the source of supply of piston-driven aircraft engines has diminished while the demand for air-boats has increased. Therefore, it has become necessary to consider the use of engines other than aircraft engines to power these air-boats.
Automotive engines and the repair parts therefore are generally and readily available as a potential source of power for air-boats. However, the output of an automobile engine, in terms of the designed revolutions per minute (rpm) of the crank shaft, is greater than the designed or manufacturer's recommended rotational speed of a pusher-type propeller used to power air-boats. These pusher-type propellers are frequently formed of a laminated wood, with a stainless steel tip which is not safe or efficient to run in excess of 3,000 rpm top speed. Therefore, in order to couple the output from an automotive engine to a pusher-type propeller, the output from the automotive engine must be coupled to the pusher-type propeller in a manner to meet both the automotive engine manufacturer's specification for safe and efficient operation, and the manufacturer's specifications for the operation of a pusher-type propeller to achieve the maximum push power at which the propeller is operated.
Automotive engines, also are designed for rotational movement of the crank shaft free from any axial loading. In the operation of any type of propeller, an axial load is applied to the engine when rotational movement is imparted whether the propeller is of a tractor or pusher type. Therefore, in order to utilize an automotive engine for an air-boat application, accommodation must be made for the axial loading which must be applied by the pusher-type propeller to the automotive engine.
Another consideration which must be accommodated is the safety of the air-boat operator, and those persons in the areas wherein such air-boats are operated. When a propeller is being driven by an aircraft engine for flight, the propeller is not generally operated in an environment wherein the propeller is exposed for contacting any solid objects. Therefore, such aircraft propellers are secured to an output drive shaft of the engine for rotation therewith. In the event that the output drive shaft would fail, the axial force loading created by the rotational movement of the propeller would cause the propeller to separate from the engine, and go free-wheeling through space until the propeller crashes to the ground. The frequency with which a propeller might strike a solid object creating such circumstances when in flight, is extremely rare. In the event that such an occasion would occur, creating a "fly-away" propeller, such an event would create a safety hazard. However, the frequency with which such occasions might occur is so low that propellers are fastened directly to the output drive shaft of aircraft engines without any provision to prevent such an occurrence.
In the operation of air-boats, however, such boats are frequently operated in swampy areas with overhanging tree limbs. While provisions are made to engage the rotating prop, these propellers can come into contact with solid objects such as tree limbs or overhanging branches. Therefore, the frequency with which the propeller on an air-boat can be broken and/or cause the output drive shaft to break is far greater than when a propeller is used to power an aircraft in flight. When such "fly-away" propellers occur, the propellers create an extremely dangerous situation to the air-boat operator and those persons in the area. If, however, the occurrence of fly-away propellers is prevented, such a failure would at most be an inconvenience, since the air-boat would just remain afloat until such time as servicing or towing help arrived.
The present invention permits an automotive engine to be coupled to a pusher-type propeller for use in an air-boat. The pusher-type propeller is mounted to an output drive shaft of a gear box in a manner such that in the event the propeller strikes a solid object breaking the output drive shaft, the propeller will be retained in its original orientation and cannot become a "fly-away" creating a safety hazard.